Making a Diagnosis
Making a Diagnosis
Antinuclear antibody (ANA)
Commonly found in the blood of people who have lupus, ANAs (abnormal antibodies directed against the cells' nuclei) can also suggest the presence of polymyositis, scleroderma, Sjögren's syndrome, mixed connective tissue disease or rheumatoid arthritis. Tests to detect specific subsets of these antibodies can be used to confirm the dignosis of a particular disease or form of arthritis.
Rheumatoid factor (RF)
Designed to detect and measure the level of an antibody that acts against the blood component gamma globulin, this test is often positive in people with rheumatoid arthritis.
Uric acid
By measuring the level of uric acid in the blood, this test helps doctors diagnose gout, a condition that occurs when excess uric acid crystallizes and forms deposits in the joints and other tissues, causing inflammation and severe pain.
HLA tissue typing
This test, which detects the presence of certain genetic markers in the blood, can often confirm a diagnosis of ankylosing spondylitis (a disease involving inflammation of the spine and sacroiliac joint) or Reiter's syndrome (a disease involving inflammation of the urethra, eyes and joints). The genetic marker HLA-B27 is almost always present in people with either of these diseases.
Erythrocyte sedimentation rate
Also called ESR or "sed rate," this test measures how fast red blood cells cling together, fall and settle (like sediment) in the bottom of a glass tube over the course of an hour. The higher the rate, the greater the amount of inflammation.
Lyme serology
This test detects an immune response to the infectious agent that causes Lyme disease and thus can be used to confirm a diagonsis of the disease.
Skin biopsy
Taking small samples of skin and examining them under a microscope can help doctors diagnose forms of arthritis that involve the skin, such as lupus, vasculitis (inflammation of the blood vessels) and psoriatic arthritis.
Muscle biopsy
By going a little deeper into the tissue than with the skin biopsy, the surgeon can take a sample of muscle to be examined for signs of damage to the muscle fibers. Findings can confirm a diagnosis of polymyositis or vasculitis.
Joint fluid tests
In this procedure, which is similar to drawing blood, the doctor inserts a needle into a joint space and removes fluid. An examination of the fluid may reveal uric acid crystals, confirming a diagnosis of gout, or bacteria, suggesting that the joint inflammation is caused by infection.
